1. Field of the Invention
This invention relates to an alignment structure for an optical assembly. The optical assembly may be attached to an exposure apparatus in a photolithography process to manufacture semiconductor wafers. More particularly, the present invention relates to a kinematic spacer and a set of flexures which can be placed between two adjacent lens cells in the optical assembly to control axial and radial alignments of the lens cells along an optical axis of the optical assembly.
2. Description of the Related Art
A lens barrel is a tubular mechanical structure containing a series of lenses which are aligned to transfer an image from one end of the lens barrel to the other. The lens barrel may include a sturdy threaded body and durable metal retaining rings, often referred to as sub-barrels, to carry a series of lens holders, commonly referred to as cells.
Two conventional optical barrel structures are currently available in the market. A first type of conventional lens barrel carries a plurality of lens holders on which lenses are mounted. The lens holders are stacked in a serial orientation along an optical, axis of the lens barrel and slidably fit inside the lens barrel. This structure is commonly referred to as the barrel type. A second type of lens barrel comprises a series of sub-barrels connected end to end by fasteners. This structure is referred to as the sub-barrel type. In both types of conventional optical barrels, the barrel and the sub-barrels are commonly made of brass because brass is relatively inexpensive and easy to machine to achieve components with high tolerances.
Both optical barrel types are commonly used in optical assembly. For example, an optical assembly having a lens barrel may be used in an exposure apparatus for production of semiconductor wafers. The exposure apparatus includes a reticle positioned near an entrance end of the lens barrel and a semiconductor wafer positioned near an exit end. The reticle defines a pattern of signal paths to be etched on a semiconductor wafer. The exposure apparatus shines light through the reticle, and transfers the pattern through the lens barrel onto a predetermined area on the semiconductor wafer. The semiconductor wafer is a silicon wafer with a photo-sensitive coating for making semiconductor devices, such as microprocessor or memory chips.
Commonly, an optical lens barrel, either the barrel type or the sub-barrel type, includes a plurality of lens cells carrying a plurality of lenses having various characteristics. The lens cells are serially aligned along the optical axis of the lens barrel. A washer is often used between adjacent lens cells to space the cells apart from each other. The washer is an annular flat ring having two opposing flat surfaces. Each flat surface facilitates full-surface contact with the adjacent lens cell.
A common problem with lens barrels is that lens cells often do not align properly both in the axial and radial direction with respect to the optical axis of the lens barrel. In addition, the lens barrel structure may need to be repeatedly disassembled to replace the lenses. The lens cells often do not align properly when reassembled. Therefore, a primary consideration for this type of optical barrel structure includes designing components for an optical lens barrel which are capable of holding high tolerances and accurate alignment even when the optical barrel structure is repeatedly disassembled and reassembled.
In light of the foregoing, there is a need for an alignment structure for use as an attachment to the lens barrel, as well as an aligning method, to control accurate alignment of the axially aligned components carried in the lens barrel.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to a kinematic alignment structure. The alignment structure may be used as an attachment inside a cylindrical body which carries a plurality of axially aligned components. An example of such a cylindrical body applying the principles of the present invention includes an optical lens barrel carrying a plurality of lens cells. The alignment structure comprises a spacer ring having two opposing surfaces and a plurality of support protrusions positioned on one of the two opposing surfaces. The spacer ring is rotatable around the axial direction to position the support protrusions to control the axial alignment of the components. Additionally, the alignment structure may further comprise an article holder having a plurality of centering flexures. The plurality of centering flexures are equi-angularly positioned on the outer circumference of the article holder to adjust the article holder in a radial direction.
The present invention is also directed to a method for kinematically aligning a plurality of components which are axially aligned and carried in a cylindrical body. The method comprises the step of providing a spacer ring having two opposing surfaces and a plurality of support protrusions positioned on one of the two opposing surfaces, and rotating the spacer ring around the axial direction to position the support protrusions to control the axial alignment of the components. The method may also include a step of providing an article holder to adjust the article holder in a radial direction. The article holder has an outer circumference and a plurality of centering flexures. The centering flexures are equi-angularly positioned on the outer circumference to control the radial alignment of the article holder within the cylindrical body. The method may also include a step of aligning the plurality of centering flexures with corresponding alignment marks on the inner surface of the cylindrical body to facilitate consistent alignment during an assembly process.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The objects and advantages may be obtained by means of the combinations set forth in the attached claims.